1. Field of the Invention
The invention relates to process and apparatuses for applying glue, and more particularly to a process and apparatus for controllably applying glue or another matrix material to continuous threads.
2. Discussion of the Related Art
In many commercial applications, it is desirable to effectively bond thread to another structure while using a minimal amount of adhesive. One such application involves the production of baby diapers. Diaper pants are composed of an essentially rectangular sheet-like structure which has a highly pliable impermeable film on the outside and an absorbent pad on the inside. Elongate leg cutouts are provided on the two longitudinal sides. Those regions of the diaper pants which project beyond the leg cutouts in the longitudinal direction are wrapped round the body at the front and rear and bonded together at the sides by means of an adhesive-film blank provided on the diaper pants.
The leg cutouts are intended to mold themselves to the leg gently, but sealingly, so that no fluid can escape at this location. To achieve this flexibility, the sheet-like structure is creped in the region of the leg cutouts and is thus elastically stretchable. The creping is obtained by means of one or more elastomeric threads which are arranged next to one another in the longitudinal direction within the edge of the leg cutout and which, in the stretched state, are bonded to the sheet-like structure over their entire length in the region of the leg cutouts. There should be no bonding in the regions projecting beyond the leg cutouts in the longitudinal direction, so that these regions are not creped and can be folded flat. Among other things, the elastomeric threads can be composed of rubber material or of textile material which, as a result of texturing, has acquired elastomeric properties in the longitudinal direction. An example of the latter is Lycra.RTM., commercially available from E.I. Du Pont de Nemours and Company.
There are two known processes for bonding the elastomeric threads to the sheetlike structure of the diapers. In the first process, a glue track is formed on the sheet-like structure, and the elastomeric threads are pressed under prestress into this glue track. This process, however, is unsatisfactory, because the glue does not adhere well to the elastomeric threads. Furthermore, due to the glue track, a hardening of the sheet-like structure occurs in a zone where it is least desirable, that is, in the region of the edge of the leg cutouts.
In another process, the glue is applied to the threads by drawing these through a glue supply. As before, the adhesion of the threads to the sheetlike structure is unsatisfactory, because the threads do not readily accept the glue and frequently only individual, intermittent glue drops are caught on the thread.